1. Field of the Invention
The present invention relates to a routing system for receiving a datagram (packet) addressed to a mobile node and forwarding the received datagram to a relevant mobile node on the basis of a home address and a care-of address.
2. Description of the Related Art
Standardization of Mobile IPv6 (Internet Protocol version 6) as a protocol related to the mobile node (MN) in an IP network, has been promoted over the recent years. Mobile IPv6 is defined as a protocol that enables the mobile node to seamlessly perform communications even when changing its location of a network link (visiting a foreign network).
FIG. 28 is a diagram showing an outline architecture of a system P1 utilizing Mobile IPv6. The system P1 utilizing Mobile IPv6 will be explained referring to FIG. 28.
The system P1 includes a mobile node P2, a home agent (HA) P3, a home link (home network) P4, a foreign link P5 and a network P6 that connects the home link P4 and the foreign link P5 to each other in a communicable manner. To start with, the mobile node P2 and the home agent P3 will be described.
The mobile node P2 is configured by use of a mobile IP terminal device. The mobile node P2 is normally connected to the home link P4 and has a home address used in the home link P4. The mobile node P2, when visiting the foreign link P5, performs the communications by use of an address (a care-of address) assigned to the mobile node P2 itself in this visited foreign link P5. At this time, the mobile node P2 stores its built-in storage device with the home address and the care-of address. Further, the mobile node P2 requests the home agent P3 in the home link P4 to store the care-of address and the home address in a way that maps these addresses to each other.
Moreover, the mobile node P2, when returning to the home link P4 from the foreign link P5, notifies the home agent P3 that the mobile node P2 itself resides in the home link P4.
The home agent P3 manages the mobile node P2 normally connected to the home link P4 to which the home agent P3 itself is attached. To be specific, the home agent P3 receives (intercepts) a packet (datagram) addressed to a managing target mobile node P2, and forwards this packet to a mobile node P2 defined as a forward destination of this packet.
The home agent P3 has a binding cache (BC). The home agent P3 stores the binding cache with the care-of address used by the mobile node P2 in the foreign link P5 in a way that maps this care-of-address to the home address of this mobile node P2. Further, the home agent P3, when receiving from the mobile node P2 a notification that the mobile node P2 is located in the home link P4, deletes the home address of the mobile node P2 and the care-of address mapping thereto, which are stored on the binding cache.
Next, an example of operation of the system P1 utilizing Mobile IPv6 will be discussed. The mobile node P2 has the home address used in the home link P4. Hence, the mobile node P2, when located in the home link P4, performs the communications using the home address.
The mobile node P2 moves to the foreign link P5 while being carried by a user and connects to the foreign link P5. The mobile node P2 is unable to perform the communications using the home address in the foreign link P5. Therefore, the mobile node P2 obtains a care-of address used in the foreign link P5. Then, the mobile node P2 sends a BU message (Binding Update message: location information registration message) to the home agent P3 attached to the home link P4 to which the mobile node P2 normally connects. Thus, the mobile node P2 performs the communications using the care-of address in the foreign link P5.
The BU message contains the care-of address and the home address. The home agent P3 receiving the BU message registers a binding cache with a binding cache (BC) entry in which the care-of address and the home address contained in the BU message are made mapping to each other. Further, the home agent P3, when receiving the BU message, sends a BA message (Binding Acknowledgement message: location information registration acknowledgement message) to the mobile node P2 as a sender of this BU message.
The home agent P3, when receiving the packet addressed to the mobile node P2, searches for a BC entry about this mobile node P2 after detecting whether this. BC entry is stored in the binding cache or not. At this time, the home agent P3 judges the mobile node P2 as a forward destination of this packet by referring to a destination address contained in the header of the received packet. Further, the home agent P3 searches through the binding cache with this destination address used as a search key. If the BC entry about this mobile node P2 is stored therein, the home agent P3 forwards the received packet to the care-of address in this BC entry. Whereas if the BC entry about this mobile node P2 is not stored, the home agent P3 forwards this packet to the destination address contained in the packet.
Thus, according to the system P1 utilizing Mobile IPv6, the packet addressed to the mobile node P2 is transmitted via the home agent P3. Therefore, in a state where the home agent P3 falls into a system-down, the packet addressed to the mobile node P2 is discarded with reaching the mobile node P2. Accordingly, a redundancy is required of the home agent P3.
In the system utilizing Mobile IPv6, there have hitherto been a DHAD algorithm (Dynamic HA Discovery algorithm) and a clustering technique as technologies for giving redundancy to the home agent P3. The following is a description of each of these technologies.
According to the system utilizing the DHAD algorithm, a plurality of home agents P3 are installed in one single home link P4. The home agent P3 periodically communicates with each of other home agents installed in the same home link P4, thus mutually confirming availability of each of the home agents P3. Then, the home agent P3 sets a priority of each home agent and creates a priority list. The home agents P3 installed in the same home link P4 have the unified (same) priority list.
One of the plurality of home agents P3 is assigned to the mobile node P2. The mobile node P2 sends the BU message to the assigned home agent P3.
If a fault occurs in the home agent P3, the mobile node P2 having sent the BU message to this home agent P3 is unable to receive a BA message to this BU message, with the result that a timeout occurs. At this time, the mobile node P2 judges that the fault occurs in the home agent P3 as a forward destination of the BU message. Then, the mobile node P2 sends, to the home link P4, by anycasting a priority list request for transmitting the priority list, and obtains the priority list from any one of the home agents P3. The mobile node P2 selects, based on the priority list obtained, the home agent P3 exhibiting a high priority and sends the BU message to this home agent P3. Thus, the DHAD algorithm actualizes the redundancy of the home agent P3.
According to the system utilizing the clustering technique, the plurality of home agents P3 are installed on one single home link P4. The home agent P3 periodically exchanges control information mutually with other home agents P3, thus taking synchronization among pieces of control information. The control information is information necessary for an operation as the home agent, including the binding cache. If the fault occurs in a certain home agent P3, one of other home agents P3 takes over a MAC address (Media Access Control address) and an IP address of the home agent P3 in which the fault occurred. Then, this home agent P3 operates as a substitute device for the fault-occurred home agent P3.